There are many different technologies currently used to build physical three-dimensional models using additive manufacturing technology, e.g. building a model layer by layer. Typically, a virtual design of the three-dimensional model, e.g. represented through computer-aided design (CAD) software or the like, is transformed into a plurality of thin (quasi-two-dimensional) cross-sectional layers which are built on one another in succession.
There are a number of known ways in which the cross-sectional layers may be formed. For example, it is known to sinter a selected sub-region of a deposited area of green material, e.g. by guiding a laser beam over the sub-region. Such an arrangement is disclosed in WO 2004/056512. Another example involves the use of a two-dimensional heat or light source arranged to melt or cure all of a selected sub-region at the same time by masking out the areas not to be melted. Such an arrangement is disclosed in US 2002/0149137.
WO 2011/045291 discloses a three-dimensional printer in which a three-dimensional model is built by sequential deposition of a plurality of cross-sectional layers by using a thermal print head movable relative to a material bed. This device is suited for use with flowable build material, such as polyamide powder. To create the layer of powder to be treated with the thermal print head, a heap of powder is deposited at one end of the material bed and spread over the material bed by a suitable platform and compacted by a pressure plate or the like.
US 2010/0151136 discloses another three-dimensional printer in which models are built by the heat treatment of sequential layers of powdered build material. In this case, the powder for each layer is transported from a build powder container to the material bed on a slat. The slat in attached to a conveyor belt which moves it on a path through the build powder container, where it collects the powder, to the material bed. The conveyor belt is then arranged to upend the slat at the material bed to deposit the collected powder in a heap to be spread into the layer before the printing process begins.
EP 2 450 177 discloses a further example of a three-dimensional printer in which models are built by the heat treatment of sequential layers of powdered build material. In this case, the powder for each layer is transported pneumatically from a powder chamber to a dispensing hopper, from where it can be deposited in a heap on the material bed and spread into a layer in a conventional manner.